<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        p{
            color: red;
        }
        .content{
            color: blue;
        }
        .size{
            font-size: 79px;
        }
    </style>
</head>
<body>
    <p>haha</p>
    <p>heihei</p>
    <p class="content">emoji😁</p>
    <!-- 一个元素可以有多个类，用空格隔开 -->
    <h3 class="content size">This is a heading</h3>
</body>
</html>